1. Field of the Invention
The present invention relates to a vehicle diagnosing apparatus which diagnoses a vehicle via an electronic control unit (ECU) which is mounted on the vehicle.
2. Description of the Related Art
As this kind of vehicle diagnosing apparatus, there has hitherto been known the following one in Japanese Published Examined Patent Application No. 18780/1995. Namely, the vehicle diagnosing apparatus is connected to an electronic control unit which is mounted on a vehicle, and the vehicle is diagnosed by incorporating (or receiving), via the electronic control unit, detected signals from various sensors which are disposed in the vehicle. When a signal which demands the transmission of data is transmitted from the vehicle diagnosing apparatus to the electronic control unit, the detected signals from the sensors that meet the requirements of the demand are transmitted to the vehicle diagnosing apparatus. The vehicle is then diagnosed based on the detected signals.
There has also been known the following vehicle diagnosing apparatus in Japanese Published Examined Patent Application No. 18779/1995. Namely, for example, the state (or condition) of depressing an accelerator pedal, and an air/fuel ratio which is obtained by a signal detected by an O.sub.2 sensor are respectively detected as digitized data. If the air/fuel ratio is switched from a lean state to a rich state by a change in the state of depressing the accelerator pedal from a non-depressed condition to a depressed condition, a judgement is made that the vehicle is in a normal condition.
In the former example of the above-described conventional apparatuses, it is necessary to set in advance, before the vehicle is diagnosed, the timing of transmitting the signal which demands the transmission of data. For example, in case the timing of incorporating the detected signals is set theoretically by making the lapse of time to serve as a parameter, it is necessary to make the setting, by referring to the design data of the vehicle, such that the detected signals can be incorporated surely and stably at timings with sufficient allowance in time. Therefore, it requires unnecessarily long time before the incorporation of the detected signals is completed, with the result that the diagnosing time becomes long. It is conceivable to continuously incorporate the detected signals from various kinds of sensors over a wide range prior to the diagnosing and then to set in advance the most appropriate timings of incorporating the detected signals from the state of changes in the detected signals. However, this solution requires a separate apparatus for the purpose of setting the timings.
In the latter example of the above-described conventional apparatuses, on the other hand, since the diagnosing is performed by means of digitized data, a judgement cannot be made about the timing at which the digitized data are switched. It follows that an accurate diagnosing cannot be performed. In other words, for example, even if the air/fuel ratio is judged to have been switched to the rich state by depression of the accelerator pedal, the vehicle cannot surely be judged to be normal unless there is known the timing at which the lean state is switched to the rich state.
Therefore, in view of the above-described problems, the present invention has an object of providing a vehicle diagnosing apparatus in which the detected signals can be incorporated at most appropriate timings without using a separate apparatus and in which a more accurate diagnosing than the diagnosing by means of digitized data can be performed.